13/16/18年托福阅读真题+答案解析:What Controls Flowering

13/16/18年托福阅读真题+答案解析:What Controls Flowering

托福阅读What Controls Flowering分别在2013年1月，2016年6月18日和2018年9月9日考过，具体的详情和答案解析一起来看一下吧。

The timing of flowering and seed production is precisely tuned to a plant's physiology and the rigors of its environment. In temperate climate plants lost flower early enough so that their seeds can mature before the deadly winds of autumn. Depending on how quickly the seed and food develop flowering may occur in spring as it does in oaks; in summer as in lettuces; or even in autumn as in asters.

1. The word "rigors" in the passage is closest in meaning to

A/characteristics

B/advantages

C/stability

D/difficulties

1/D

本题为词汇题。“rigor”的意思是“严酷”，词汇所在句子“The timing of flowering and seed production is precisely tuned to a plant's physiology and the rigors of its environment.”的意思是“植物的生理机能和环境的严峻程度，精确地控制着植物开花的时机和种子的产生。” A 选项：characteristics 意思是“性质;特性”。排除。 B 选项：advantages 意思是“优势;优点”。排除。 C 选项：stability 意思是“稳定性;稳固”。排除。 D 选项：difficulties 的意思是“难度;困难”，意思最为贴近，故为正确答案。

2. The word "precisely" in the passage is closest in meaning to

A/severely

B/quickly

C/exactly

D/efficiently

2/C

本题为词汇题。“precisely”的意思是“精确地”,词汇所在句子“The timing of flowering and seed production is precisely tuned to a plant's physiology and the rigors of its environment.”的意思是“植物的生理机能和环境的严峻程度，精确地控制着植物开花的时机和种子的产生。” A 选项：severely 的意思是“严重地;严厉地”,排除。 B 选项：quickly 的意思是“迅速地”,排除。 C 选项：exactly 的意思是“正确地”，意思最为贴近，故为正确答案。 D 选项：efficiently 的意思是“高效地”，排除。

3. Paragraph 1 suggests which of the following are the seeds of asters in temperate climate?

A/They mature a short time after the plant blooms.

B/They begin to develop in autumn and mature in winter.

C/They were more plentiful than those of oaks or lettuces.

D/They are not designed to survive temperate climate.

3/A

本题为推理题。根据题干中的关键词“in temperate climate”,我们定位到本段第2句话“In temperate climate plants lost flower early enough so that their seeds can mature before the deadly winds of autumn.”意思是“在温带气候环境中，植物花朵早早凋落，这样它们的种子就能在秋天的狂风到来之前成熟。”所以我们推测，在温带气候环境中的紫苑花期一定很短，为的是在秋天之前种子能成熟。故 A 选项正确。B、C、D 选项在文中都没有提到相关的线索或内容。

What environmental cues do plants use to determine the seasons? Most cues such as temperature or water availability are quite variable: autumn can be warm; a late snow could fall in spring; also summer might be unusually cool and wet. So the only reliable cue is day length: longer days always mean that spring and summer are coming; shorter days foretell the onset of autumn and winter.

With respect to flowering botanists classify plants as day neutral, long day or short day. A day neutral plant flowers as soon as it has sufficiently grown and developed regardless of the length of day. The neutral plants include tomatoes, corn, snapdragons and roses. Although the naming is traditional, long day and short day plants are better described as short night and long night plants because their flowering actually depends on the duration of continuous darkness rather than on day length. Short night plants (which include lettuces, spinach, iris, clover and petunias) flower when the length of darkness is shorter than a species' specific critical period. Long night plants(including asters, potatoes, soy beans, goldenrod and cockleburs) flower when the length of uninterrupted darkness is longer than the species' specific critical period. Thus spinach is classified as a short night plant because it flowers only if the night is shorter than eleven hours (its critical period), and the cocklebur is a long night plant because it flowers only if an uninterrupted darkness lasts more than 8.5 hours. Both of these plants will flower with ten-hour nights.

Plant scientists can induce flowering. Plant scientists can induce flowering in the cocklebur by exposing leaves to long nights (longer than its 8.5 hour critical period) in a special chamber, while the rest of the plant continues to experience short nights. Clearly, a signal that induces flowering transmitted from the leave to the flowering bud. Plant physiologists have been attempting for decades to isolate these elusive signaling molecule often called florigen (literally, flowering maker). Some researchers believe they are close to demonstrating a flower's stimulating substance for specific type of plant. Using genetic manipulation, it is likely, however, that interactions among multiple and yet unidentified planthormones stimulate or inhibit flowering, and that these chemicals may differ among plant species. Researchers have had more success in determining how plants measure the length of uninterrupted darkness, which is a crucial stimulus for producing whatever substance control flowering.

To measure continuous darkness, a plant needs two things: some sort of metabolic clock to measure time (the duration of darkness) and a light detecting system to set the clock. Virtually all organisms have an internal biological clock that measures the time even without environmental cues. In most organisms including plants, the biological clock is poorly understood, but we know that the environmental cues, particularly light, can reset the clock. How do plants detect light? The light detecting system of plants is a pigment in leaves called phytochrome (literally, plant color).

Plants seem to use the phytochrome system in combination with their internal biological clocks to detect the duration of continuous darkness. Cockleburs, for example, flower under the schedule of sixteen hours of darkness and eight hours of light. However, interrupting the middle of the dark period with just a minute or two of lights prevents flowering. Thus their flowering is controlled by the length of continuous darkness. It is evident that even brief exposure to sunlight or white light will reset their biological clocks. The color of the light used for the light exposure is also important. A nighttime flash of pure red light inhibits flowering, while flash of light at the far-red end of the spectrum has no effect on flowering, as if no light were detected.

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